Red Hat Linux 7 Unleashed

By William Ball

• Table of Contents
  • Copyright
  • About the Lead Authors
  • About the Contributing Authors
  • Acknowledgments
  • Tell Us What You Think!
  • Introduction
  • I. Red Hat Linux Installation and User Services
  • Chapter 1. Introduction to Red Hat Linux
  • Chapter 2. Installation of Your Red Hat System
  • Chapter 3. LILO and Other Boot Managers
  • Chapter 4. Configuring the X Window System, Version 11
  • Chapter 5. Window Managers
  • Chapter 6. Connecting to the Internet
  • Chapter 7. IRC, ICQ, and Chat Clients
  • Chapter 8. Using Multimedia and Graphics Clients
    • Linux Graphic Utilities
    • Common Graphics Formats
    • Basic Graphic Editing Clients
    • Using the GIMP
    • Displaying and Printing Graphics
    • Configuring Sound
    • Playing Audio CDs
    • Playing .mp3s
    • Playing Video
    • Using a Web Cam
    • Summary
  • II. Configuring Services
  • Chapter 9. System Startup and Shutdown
  • Chapter 10. SMTP and Protocols
  • Chapter 11. FTP
  • Chapter 12. Apache Server
  • Chapter 13. Internet News
  • Chapter 14. Domain Name Service and Dynamic Host Configuration Protocol
  • Chapter 15. NIS: Network Information Service
  • Chapter 16. NFS: Network Filesystem
  • Chapter 17. Samba
  • III. System Administration and Management
  • Chapter 18. Linux Filesystems, Disks, and Other Devices
  • Chapter 19. Printing with Linux
  • Chapter 20. TCP/IP Network Management
  • Chapter 21. Linux System Administration
  • Chapter 22. Backup and Restore
  • Chapter 23. System Security
  • IV. Red Hat Development and Productivity
  • Chapter 24. Linux C/C++ Programming Tools
  • Chapter 25. Shell Scripting
  • Chapter 26. Automating Tasks
  • Chapter 27. Configuring and Building Kernels
  • Chapter 28. Emulators, Tools, and Window Clients
  • V. Appendixes
  • A. The Linux Documentation Project
  • B. Top Linux Commands and Utilities
  • C. The GNU General Public License
  • D. Red Hat Linux RPM Package Listings

Common Graphics Formats

Computer graphics are used for Web page design and report documents, and they are also used by engineers, by computer artists (designers or photographers), and even by medical researchers and practitioners. Some graphics development tasks have only modest hardware and software requirements, whereas others, such as floating-point–intensive 3D renderings and raytracings, may require specialized equipment, such as graphics cards with 64MB or more video RAM, large (19'' or larger) monitors, enormous amounts (512MB or more) of RAM, and fast CPUs. This section covers simpler graphics formats for home desktop and small business users.

Table 8.1 lists most of the types of graphics included with Red Hat Linux. You may find some new terms and acronyms, but in general, under Linux as well as other operating systems, graphics files are defined according to format, resolution, and color depth. Whereas black-and-white images are represented by resolution, or the number of pixels (dots) wide and high, and a simple "on" or "off" two-color scheme, color images may vary according to not only resolution, but the number of colors used by the graphics file. Typically, early graphics files used 16, 32, 64, or 256 colors. However, today many graphics images are stored in thousands and millions of colors (although the human eye is said to be able to distinguish only 160,000 distinct colors, many graphics monitors will only display thousands of colors, and most humans can only distinguish 30 levels of gray). Some pixel formats use three bytes of storage to represent red, green, and blue values to represent the color of each pixel of an image.

Note that not all graphics formats in Table 8.1 are pixel-oriented. Some, like PostScript, are based on page description and line drawing, creating vector-based graphics. If you view PostScript graphics in a text editor, such as emacs, you can read the "language" that describes the document. On the other hand, most pixel-based formats are binary only and unreadable.

What does this mean to the user? In general, 2D pixel-based graphics files will require ever-larger amounts of memory and hard drive storage as the resolution and color depth increase. To help stave off these requirements, many formats, such as JPEG and PNG, incorporate compression, or the removal of redundant and unneeded information in the file.

Table 8.1. Common 2D Graphics Formats

There are also many types of 3D graphics formats. In the recent past, creating, editing, rendering, or displaying pictures using 3D software required high-end computational resources. Today, you'll find a number of Open Source 3D engines, applications, editors, games, software libraries, modeling clients, and visualization systems available for Linux. However, you'll still need a compliant graphics card and proper X11 driver support for your card in order to use this class of software. One of the best places to look for an index of 3D hardware and software for Linux is http://www.linux3d.org/.

The ability to use advanced modeling and rendering software and hardware is a relatively new development for Linux, but developers and manufacturers are picking up the pace as new software is ported to the Linux platform and new graphics cards are brought to market. Some of these software packages can have enormous resource requirements, so expect only modest performance, even on 450MHz Pentium-class computers, even if you have a capable graphics card! Few, if any, laptop users will be able to take advantage of this class of software and graphics until further advances are made in graphics chipset design, CPU speed, hard drive storage, and memory.

Converting Graphics

Fortunately, most desktop PC users don't need high-end graphics cards, monitors, CPUs, and software to work with graphics. Linux comes with hundreds of simple graphics applications that may be used to create, edit, and translate graphics without the need for loading a large application and windowing client. Many of the graphics commands discussed in this section don't even require a running X11 session!

Table 8.2 lists commands that may be used to read, convert, or save graphics files. Most commands will work from the command line, while others, such as the GIMP (see Using the GIMP later in this chapter) must be run during an X11 session. Most of the commands belong to several distinct "families" from one or more developers:

• Portable anymap commands (bitmaps, graymaps, pixmaps), developed by Jeff Poskanzer, are used from the command line or in shell scripts to convert files from one graphic format to another. There are nearly 100 commands included in this software package.
• The convert command, by John Cristy, is part of the ImageMagick software package (included with Red Hat Linux, and which has a graphical X11 client named display), and can be used to "convert" graphics; this capable command has the ability to deal with nearly 70 graphics formats!
• The GIMP, by Spencer Kimball and Peter Mattis, is a comprehensive, sophisticated, and complex graphics editing client for X11, but does not convert graphics using the command line.
• The xv client by John Bradley is a free-for-personal-use graphics client that may be used from the command line or as a graphical client during an X11 session. However, this client has more than 100 command-line options with a formidable syntax. Although no longer included on Red Hat's CD-ROMs, xv is available for download at ftp://ftp.redhat.com/pub/redhat/powertools/.
• The GNOME ee client, which requires X11, will read and save graphics files in a variety of formats. This is also true of the pixie client, developed for the K Desktop Environment.

The convert command is one of the most flexible and useful graphics conversion commands included with Red Hat Linux. This command may be use to translate graphics formats on-the-fly using filename extensions. For example, to convert the graphic kitty.gif from GIF format to PCX format, use the convert command like this:

   # convert kitty.gif kitty.pcx

After you press Enter, the convert command will create a new file in the desired format with name kitty.pcx, leaving the original untouched.

Table 8.2. Linux Graphics Formats and Conversion Programs

Many of the programs listed in Table 8.2 that work with the command line may also use input-output redirection, along with pipes on the command line. For example, if you have a file named foo.pcx in PCX format, but would also like a copy in GIF and TIFF formats, you can combine the output of various commands, such as pcxtoppm, ppmtogif, giftopnm, and pnmtotiff like this:

   # pcxtoppm foo.pcx | ppmtogif | tee foo.gif | giftopnm | pnmtotiff >foo.tif

This command line, which also uses the tee command to siphon off output from the ppmtogif command, creates two copies of the original file, one named foo.gif in GIF format and the other named foo.tif in TIFF format.

Linux also comes with a number of command-line programs that may be used to perform other manipulation tasks, such as cropping, resizing, and flipping horizontally or vertically. See the man pages for the pnmcrop, pnmcut, pnmenlarge, pnmflip, pnminvert, pnmrotate, or pnmscale commands.

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